How many SIP signaling dialog(s) took place in this SIP message exchange between two SIP user agents?

Refer to the exhibit.

How many SIP signaling dialog(s) took place in this SIP message exchange between two SIP user agents?

A.
1

B.
2

C.
3

D.
4

E.
5

F.
6

Explanation:
The two common methods to determine whether a SIP session is active; RTP/RTCP
media inactivity timer and session timer have limitations when used with the Cisco UBE. The

media inactivity (rtp/rtcp) method will not work if flow around mode is configured as the media is
sent directly between endpoints without going through the Cisco UBE and session timer cannot be
used if the SIP endpoint does not support session timer.The in-dialog OPTIONS refresh feature
introduces a refresh mechanism that addresses these two scenarios, and can be used on SIP-toSIP and SIP-to-H.323 calls. The refresh with OPTIONS method is meant to only be hop-to-hop,
and not end-to-end. Since session timer achieves similar results, the OPTIONs refresh/ping will
not take affect when session timer is negotiated. The behavior on the H.323 endpoint is as if it was
a TDM-SIP call. The generating in-dialog OPTIONS is enabled at the global level or dialpeer level.
The system default setting is disabled. This feature can be use by both a TDM voice gateway and
an Cisco UBE.